Mutual Coupling Reduction of a Dual-Band Four-Port Patch Antenna With Co-Polarized Radiation Pattern by Controlling Electric Fields

Abstract

In this paper, a novel design approach to decrease the mutual coupling (MC) of a single dual-band four-port microstrip patch antenna (MPA) with a co-polarized radiation pattern is proposed via characteristic mode analysis. Initially, the traditional MPA under mode 1 to mode 4 is theoretically studied. This proves that the four modes maintain a high MC of approximately -2 dB. To address this issue, shorting pins 1 and pins 2 are inserted below the radiator, leading to a more than 12 dB MC reduction between the two ports along the x-axis. After that, the MC between the two ports along the y-axis is deeply studied. This proves that the electric field nulls of the MPA could be moved near unexcited ports and reduce the MC by combining mode 1 with mode 2 (or mode 3 with mode 4). Hence, shorting pins 3 are loaded for mode combination and low MC. In addition, shorting pins 4 are loaded to reshape the radiated fields in the upper band. Moreover, the impedance matching and bandwidth are improved by cutting the ring slots. Finally, a four-port MPA is fabricated and tested. The results show that it has satisfactorily gained a low MC of below -15 dB between the four ports in dual bands. Meanwhile, it holds low-profile, single-layer, single-element, and co-polarized radiation pattern properties.